Display screen or a portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or a portion thereof with a graphical user interface with preview window and secondary windows showing the new design.

The outer broken lines in the FIGURE show a display screen or a portion thereof that forms no part of the claimed design. The inner broken lines in the FIGURE show portions of the graphical user interface which form no part of the claimed design. The text included in the FIGURE forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or a portion thereof with a graphical user interface, as shown and described. 